1. Field of the Invention
The present invention relates to a navigation apparatus for a vehicle and an associated display method for displaying the current vehicle position in a base field and a window field formed on a display screen.
2. Description of the Prior Art
FIG. 6 shows in block diagram an example of conventional navigation apparatus disclosed in Japanese Patent Publication No. 2-46086, and FIG. 7 shows the screen of a CRT (cathode ray tube) display unit on which maps and other navigational information are displayed.
In FIG. 6, the apparatus installed in a vehicle includes a CRT (cathode ray tube) display unit 1 as a display means, a ROM (read-only memory) package 2 for storing map data, a manual operation panel 3, an electronic controller 4 which performs the map display control and the like, an azimuth sensor 10 which detects a direction of movement of the vehicle, and a distance sensor 11 which measures a running distance of the vehicle. The electronic controller 4 consists of an MPU (micro-processing unit) 5, a ROM 6, a RAM (random access memory) 7, an I/O (input/output) unit 8, a display controller 9 which controls the CRT 1. In FIG. 7, the display screen consists of a main display area 1a and a subordinate display area 1b.
Next, the operation 4 of this navigation apparatus related to the present invention will be explained on the flowchart of FIG. 8 which shows the steps of operation after the apparatus has been turned on.
In step 201, the controller 4 displays a map centered by the current vehicle position in the main display area 1a of the display screen shown in FIG. 7 and spots a mark at the current vehicle position. In step 202, the controller 4 displays a magnified detailed map including the current vehicle position in the subordinate display area 1b in the same azimuth orientation as the map of the main display area la.
As the vehicle moves, the vehicle position marks move on the maps which are fixed in the display areas. When the vehicle goes out of the map range of the subordinate display area 1b, the displayed map is revised so that the current vehicle position is located at the center of the subordinate display area 1b.
Maps are displayed, with the north always facing upward, and therefore the driver of the vehicle is liable to confuse in making a right turn or a left turn, except when the vehicle is running upwardly on the screen. On the other hand if maps are displayed, with the vehicle moving direction facing upward, it would be difficult for the driver who is accustomed to north up-facing maps to recognize the current vehicle position on the displayed map.